Conventionally, as a light irradiation device used in an additive layer manufacturing apparatus, a device configured to irradiate jetted-out powdery material with a light beam and cause the material to melt has been known.
The light irradiation device for an additive layer manufacturing apparatus needs to be structured such that a function unit does not block off the light beam. Thus, in the conventional structure, the layout of the function unit has been greatly restricted. Consequently, in this type of light irradiation device, it is meaningful if a structure that can improve the degree of freedom in the layout of the function unit.